Series 3 – Scientific Landers
Part Three of the Ring of Fire Expedition is dedicated to the study of areas adjacent to Challenger Deep; areas that have traditionally been overlooked in favour of their deeper neighbour.
Augmenting their primary function of providing vital communications and positioning data to the submersible Limiting Factor, the three Scientific Landers Flere, Scaff and Closp feature an array of tools and functions for scientific enquiry.
The Science team is led by Dr Alan Jamieson, Senior Lecturer in Marine Ecology at Newcastle University, who specializes in deep and extreme environments.
Despite the Challenger Deep area of the Mariana Trench being the most well studied region of the hadal zone, the prestige of being the deepest point on Earth has drawn scientific enquiry away from the rest of the trench. There have historically been sampling campaigns in Sirena Deep, but very little anywhere else in the trench.
In terms of habitat for hadal species, that is, species limited to depths greater than 6000m, the Mariana is in fact 5 isolated areas. These areas are partitioned as seamounts from the Pacific plate are subducted into the trench.
One line of scientific enquiry is how the biodiversity and habitat characteristics differ across the partitions, and more importantly, if the same species are present, are they genetically isolated or are there mechanism for gene flow?
The bigger picture is do with scale. If we can examine populations between these areas separated only a seamount, and then between the Mariana and the neighbouring trenches such as Izu-Bonin and Japan, to trench clusters in other Pacific regions, (e.g. San Cristobal and Santa Cruz trenches, or Tonga and Kermadec trenches), to trenches in other oceans (such as the Java trench in the Indian Ocean, or South Sandwich in the Southern ocean), then we can ask questions about genetic connectivity and speciation on multiple scales. We can start to unravel what is a global function of depth (being ‘hadal’) and what is a function of local environmental conditions.
“Naming” the Deeps
In the mission we called three unnamed deeps Saipan, Rota and Tinian Deep, after the adjacent Islands. These are not official names , but for convenience sake they were used here.
On this mission we successfully deployed three landers in both the ‘Saipan’ and ‘Tinian’ Deep, six in the ‘Rota’ Deep and another six in the Nero Deep. When combined with the data we already have from Challenger and Sirena Deep we have finally a full spread of depths, latitudes and slopes in which to address the true population structure of the Mariana Trench.
Mariana Trench Video Highlights
Dr Alan Jamieson: One of our goals is to help the world better understand what’s happening at the deepest parts of the ocean.
The Supergiant amphipod (Alicella gigantea) at 5000m in the Mariana Trench, Nero Deep.
Here are a few of abyssal deep sea fish from 5800m in the northern Mariana trench, the first and last are cuck eels (Ophidiidae), the other is a grenadier (Macrouridae)
At 7200m in the Mariana trench the numbers of prawns at this site was surprisingly high. The Mariana snailfish does a nice fly-by at the end.
At 6600m in the Mariana Trench the Mariana snailfish and penaeid prawns enjoy a day out in an area of interesting geology.
A small grenadier (Coryphaenoides yaquinae) feeds at the bait and gets harassed by a cusk eel at 5000m in the Mariana Trench, Nero Deep.
Black Hole, technically known as the Sui-Shin Hole after the Suisei Seamount and the Shinsei Seamount to the north and south respectively. It is located at approximately 25˚N, 136˚E in the middle of the Philippine tectonic plate, underlying the Philippine Sea region on the Northwest Pacific Ocean.
It is a 33nm long, by 8nm wide hole and reached a maximum depth of ~6400m. To the east and west of the hole are a serious of flat plateaus decreasing in depth with distance from the hole.
The Philippine Plate
The Philippine plate is bounded by subduction trenches: the Ryukyu, Izu-Ogasawara, Mariana, Yap, Palau and Philippine trenches. These trenches are well known to host endemic hadal fauna. Recent studies in these trenches and from other areas have identified several model taxa that appear to inhabit these ultra-deep trenches at depths exceeding 6500m. The question is how do species that only live >6500m get from one trench to another if they are isolated by depths <6500m? or do they move from one to another at all?
One hypothesis was that the internal plate – the West Mariana Basin and Philippine Basin- hosts a labyrinth of networked geomorphological features that may just bed deep enough to allow gene flow, albeit limited from one trench to another. As Black Hole is in the plate centre, and is aseismic, flat bottomed, and very small it does not share many of the characteristics of the larger hadal trenches, except that is just deep enough to meet the criteria for ‘hadal’.
What we found was surprising. The model hadal species were indeed present at 6400m, the deepest depth of Black Hole, but they were only inhabiting the bottom 25 metres. There are no depths on the boundary of the Hole sufficient to allow passage from the Hole to the next nearest hadal zone, and area north around the Koho Hole. Although many other species were numerous at Black Hole, they were known and characteristic of typical abyssal-hadal transition zones of the Pacific Rim.
This data largely excludes many of the hypotheses about genetic connectivity of trenches and supports the idea that each of these deep geomorphological features host an isolated population of certain species: islands in the hadal zone.
Black Hole Video Highlights
The robust assfish, Bassozetus robustus filmed suction feeding amphipods at 6400 metres deep in Black Hole.
The cusk eel Barathrites iris scavenges bait at 6350m, 1000m deeper than previous though.
The deep water prawn Benthesicymus crenatus preys upon amphipods in Black Hole, including an impressive escape response at the end.